AoT (Attack on Tsushima) here felt like a prologue and it has a mildly intriguing spin on multiple concepts we've all seen before including the very obvious Shingeki no Kyojin inspiration, but sadly the MC is...unlikeable, because he is so mediocrely generic. He is not even someone deeply polarizing like Eren, I just couldn't care enough about Gen to hate him for being an edgy mofo or sympathize with his losses. Both the author and artist definitely tried to depict him as someone you should be able to relate to, but they failed. Rin's thicc legs and her Egon Spengler looking buddy were, honestly, more interesting than Gen. Not even his Ultraman forms managed to convince me to root for him. To me the real MCs were the JSDF soldiers and if the MC really has to be an IAS-human hybrid, it should have been Captain Okita, at least for the first era if they had really wanted to do another Terra Formars style of multi-generational plot.
As a side note, the author here is not the same as the one Tachibana worked with in Terra Formars.